Power control and handoff with power control commands and erasure indications

ABSTRACT

Techniques for performing power control and handoff are described. In an aspect, power control (PC) is supported with multiple PC modes such as an up-down PC mode and an erasure-based PC mode. One PC mode may be selected for use. Signaling may be sent to indicate the selected PC mode. If the up-down PC mode is selected, then a base station estimates the received signal quality for a terminal and sends PC commands to direct the terminal to adjust its transmit power. If the erasure-based PC mode is selected, then the base station sends erasure indications that indicate whether codewords received from the terminal are erased or non-erased. For both PC modes, the terminal adjusts its transmit power based on the power control feedback (e.g., PC commands and/or erasure indications) to achieve a target level of performance (e.g., a target erasure rate for the codewords). The erasure indications may also be used for handoff.

The present application claims priority to provisional U.S. ApplicationSer. No. 60/756,981, entitled “METHOD OF CONTROL WITH UP/DOWN COMMANDSAND ERASURE INDICATIONS,” filed Jan. 5, 2006, assigned to the assigneehereof and incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for performing power control and handoff in awireless communication system.

II. Background

A wireless multiple-access communication system can supportcommunication for multiple wireless terminals by sharing the availablesystem resources, e.g., bandwidth and transmit power. Each terminal maycommunicate with one or more base stations via transmissions on theforward and reverse links. The forward link (or downlink) refers to thecommunication link from the base stations to the terminals, and thereverse link (or uplink) refers to the communication link from theterminals to the base stations.

Multiple terminals may simultaneously receive data on the forward linkand/or transmit data on the reverse link. This may be achieved bymultiplexing the transmissions on each link to be orthogonal to oneanother in time, frequency and/or code domain. On the reverse link,complete orthogonality, if achieved, results in the transmission fromeach terminal not interfering with the transmissions from otherterminals at a receiving base station. However, complete orthogonalityamong the transmissions from different terminals is often not realizeddue to channel conditions, receiver imperfections, and so on. The lossin orthogonality results in each terminal causing some interference toother terminals communicating with the same base station. Furthermore,the transmissions from terminals communicating with different basestations are typically not orthogonal to one another. Thus, eachterminal may also cause interference to other terminals communicatingwith nearby base stations. The performance of each terminal is degradedby the interference from all other terminals in the system.

There is therefore a need in the art for techniques to control thetransmit power of the terminals to reduce interference and achieve goodperformance for all terminals.

SUMMARY

Techniques for efficiently performing power control and handoff aredescribed herein. In an aspect, power control (PC) is supported withmultiple PC modes such as an up-down PC mode and an erasure-based PCmode. One PC mode may be selected for use, e.g., based on the desiredperformance. Signaling (e.g., a PC mode bit) may be sent to indicate theselected PC mode. If the up-down PC mode is selected, then a basestation estimates the received signal quality for a terminal and sendsPC commands to direct the terminal to adjust its transmit power. If theerasure-based PC mode is selected, then the base station detectscodeworks received from the terminal and sends erasure indications thatindicate whether these codewords are erased or non-erased. For both PCmodes, the terminal adjusts its transmit power based on the powercontrol feedback (e.g., PC commands and/or erasure indications) toachieve a target level of performance (e.g., a target erasure rate forthe codewords sent by the terminal).

In another aspect, power control is achieved based on PC commands, andhandoff is achieved based on erasure indications. A terminal transmitscodewords on the reverse link. A first set of at least one base stationestimates the received signal quality for the terminal, e.g., based onthe codewords received from the terminal, and generates PC commandsbased on the received signal quality. A second set of at least one basestation generates erasure indications for the codewords received fromthe terminal. The first set may include only a serving base station. Thesecond set may include the serving base station and possibly other basestations. The terminal adjusts its transmit power based on the PCcommands received from the first set of base station(s). The terminalmay determine the erasure rate for each base station in the second set,select the base station with the lowest erasure rate, and performhandoff to the selected base station.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows a power control mechanism supporting multiple PC modes.

FIG. 3 shows a power control mechanism for the up-down PC mode.

FIG. 4 shows a power control mechanism for the erasure-based PC mode.

FIG. 5 shows a process performed by a base station for power control ofa terminal.

FIG. 6 shows an apparatus at a base station for power control of aterminal.

FIG. 7 shows a process performed by a terminal for power control.

FIG. 8 shows an apparatus at a terminal for power control.

FIG. 9 shows a process for performing power control and handoff.

FIG. 10 shows an apparatus for performing power control and handoff.

FIG. 11 shows a block diagram of a terminal and two base stations.

DETAILED DESCRIPTION

FIG. 1 shows a wireless communication system 100 with multiple basestations 110. A base station is a station that communicates with theterminals. A base station may also be called, and may contain some orall of the functionality of, an access point, a Node B, and/or someother network entity. Each base station provides communication coveragefor a particular geographic area. The term “cell” can refer to a basestation and/or its coverage area depending on the context in which theterm is used. To improve system capacity, a base station coverage areamay be partitioned into multiple (e.g., three) smaller areas. Eachsmaller area may be served by a respective base transceiver subsystem(BTS). The term “sector” can refer to a BTS and/or its coverage areadepending on the context in which the term is used. For a sectorizedcell, the BTSs for all sectors of that cell are typically co-locatedwithin the base station for the cell.

Terminals may be dispersed throughout the system, and each terminal maybe fixed or mobile. For simplicity, only one terminal 120 is shown inFIG. 1. A terminal may also be called, and may contain some or all ofthe functionality of, an access terminal (AT), a mobile station (MS), auser equipment (UE), and/or some other entity. A terminal may be awireless device, a cellular phone, a personal digital assistant (PDA), awireless modem, a handheld device, and so on. A terminal may communicatewith zero, one, or multiple base stations on the forward and/or reverselink at any given moment.

For a centralized architecture, a system controller 130 couples to basestations 110 and provides coordination and control for the basestations. System controller 130 may be a single network entity or acollection of network entities. For a distributed architecture, the basestations may communicate with one another as needed.

The power control and handoff techniques described herein may be usedfor various wireless communication systems and various radiotechnologies such as Code Division Multiple Access (CDMA), Time DivisionMultiple access (TDMA), Frequency Division Multiple Access (FDMA),Orthogonal FDMA (OFDMA), Single-Carrier FDMA (SC-FDMA), etc. OFDMAutilizes Orthogonal Frequency Division Multiplexing (OFDM), and SC-FDMAutilizes Single-Carrier Frequency Division Multiplexing (SC-FDM). OFDMand SC-FDM partition a frequency band (e.g., the system bandwidth) intomultiple orthogonal subcarriers, which are also called tones, bins, andso on. Each subcarrier may be modulated with data. In general,modulation symbols are sent in the frequency domain with OFDM and in thetime domain with SC-FDM. The techniques may also be used for wirelesscommunication systems that utilize multiple radio technologies (e.g.,CDMA, and OFDMA).

The techniques described herein may also be used for systems withsectorized cells as well as systems with un-sectorized cells. Forclarity, the techniques are described below for a system with sectorizedcells. In the following description, the terms “base station” and“sector” are used interchangeably, and the terms “terminal” and “user”are also used interchangeably.

Terminal 120 may transmit data, signaling, pilot and/or other content onthe reverse link. Transmission on the reverse link may be supported invarious manners, depending on the system design. In one design, anactive set is maintained for the terminal and includes one or moresectors that may serve the terminal on the reverse link. Sectors may beadded to or removed from the active set based on signal qualitymeasurements, which may be made by the terminal and/or the sectors. Onesector in the active set may be designed as a reverse link (RL) servingsector for the terminal. The serving sector may perform variousfunctions (e.g., scheduling, data decoding, power control, and so on) tosupport reverse link transmission for the terminal. The remainingsectors (if any) in the active set may be referred to as active setnon-serving sectors. The non-serving sectors may perform variousfunctions (e.g., feedback reporting) to assist in the selection of theserving sector.

As shown in FIG. 1, the transmission from terminal 120 may be receivedby any number of sectors. These sectors may include serving sector 110x, non-serving sectors 110 a through 110 m, and other sectors (e.g.,neighbor sector 110 n) that are not in the active set of the terminal.The transmission from terminal 120 may cause interference to otherterminals transmitting to the same serving sector 110 x as well as otherterminals transmitting to other sectors, e.g., sectors 110 a through 110n. Hence, it is desirable to control the transmit power of terminal 120such that the desired performance is achieved for terminal 120 whilereducing interference to other terminals.

1. RL Power Control

Reverse link (RL) power control refers to control of transmit power of aterminal on the reverse link. In general, RL power control may beachieved based on any RL transmission that allows the sectors toestimate the signal quality of the reverse link for the terminal. The RLtransmission may be for pilot, data, signaling, or any combinationthereof. To achieve good power control performance, the RL transmissionshould be sent regularly so that the transmit power of the terminal canbe adjusted at a sufficiently fast rate to track changes in the channelconditions.

In one design, RL power control is achieved based on codewords sent on acontrol channel by a terminal. In general, the codewords may be forvarious types of information. In one design, the codewords are forchannel quality indication (CQI) reports sent on a CQI channel. Aterminal may make signal quality measurements for the sectors in theactive set, generate CQI reports for these measurements, and transmitthe CQI reports on the CQI channel, e.g., to the serving sector. The CQIreports may be used to select a suitable sector to serve the terminal onthe forward link. In other designs, the codewords may be for other typesof information.

A CQI report (or a signaling message) may be a small word containing Lbits, where in general L≧1. This word may be mapped to one of 2^(L)possible codewords in a codebook. The codeword is then sent on the CQIchannel. The same number of bits (e.g., L bits) may be sent for each CQIreport. In this case, the same codebook may be used for each CQI report.Alternatively, different numbers of bits may be sent for different CQIreports, and different codebooks may be used depending n the number ofbits being sent. The codewords in a given codebook may be generatedbased on a block code or some other mapping scheme. In one design, the2^(L) possible codewords are formed by 2^(L) different Walsh codes oflength 2^(L). A specific Walsh code may be sent as a codeword for anL-bit CQI report.

In one aspect, RL power control is supported with multiple PC modes. ThePC modes may also be referred to as PC schemes, PC mechanisms, PCalgorithms, and so on. In one design, the multiple PC modes include anup-down PC mode and an erasure-based PC mode. In the up-down PC mode, asector (e.g., the serving sector) estimates the received signal qualityfor a terminal and sends PC commands/bits to direct the terminal toadjust its transmit power. In the erasure-based PC mode, a sector (e.g.,the serving sector) sends erasure indications/bits that indicate theresults of erasure detection at the sector for codewords received fromthe terminal. For both PC modes, the terminal adjusts its transmit powerbased on the power control feedback (e.g., PC commands and/or erasureindications) to achieve a target level of performance, which may bequantified by a target erasure rate and/or some other measures.

FIG. 2 shows a design of a power control mechanism 200 that supports theup-down PC mode and the erasure-based PC mode. In this design, servingsector 110 x sends to terminal 120 signaling that indicates the PC modeto use for RL power control. In one design, this signaling is anRLCtrlPCMode bit that may be set to either ‘0’ to indicate theerasure-based PC mode or ‘1’ to indicate the up-down PC mode. Thesignaling may be sent at the start of a communication session, wheneverthere is a change in PC mode, and so on. In another design, sector 110 xbroadcasts the PC mode supported by the sector to all terminals withinits coverage area. In any case, a signaling processor 258 at terminal120 receives the signaling from serving sector 110 x and provides a modecontrol that indicates whether to use the up-down PC mode or theerasure-based PC mode.

If the up-down PC mode is selected, then serving sector 110 xperiodically estimates the received signal quality for terminal 120 andsends PC commands via the forward link (cloud 252) to terminal 120. EachPC command may be either (1) an UP command to direct an increase intransmit power or (2) a DOWN command to direct a decrease in transmitpower. At terminal 120, an up-down PC mode processor 260 receives the PCcommands from serving sector 110 x, adjusts the transmit power ofterminal 120 based on the received PC commands, and provides transmitpower level P_(ud)(n) to a transmit (TX) data processor/modulator 280.Processor 280 transmits codewords at transmit power of P_(ud)(n) on thereverse link (cloud 250) to serving sector 110 x and non-serving sectors110 a through 110 m.

Sectors 110 x and 110 a through 110 m receive the codewords fromterminal 120. Each sector 110 decodes each received codeword andperforms erasure detection to determine whether the decoding resultmeets a desired level of confidence. A received codeword may be deemed(1) “erased” if the decoding result does not meet the desired level ofconfidence or (2) “non-erased” if the decoding result meets the desiredlevel of confidence. Each sector 110 sends erasure indications toterminal 120. An erasure indication may indicate whether a receivedcodeword is erased or non-erased.

If the erasure-based PC mode is selected, then the erasure indicationsfrom serving sector 110 x are used for RL power control. At terminal120, an erasure-based PC mode processor 270 receives the erasureindications from serving sector 110 x, adjusts the transmit power ofterminal 120 based on the received erasure indications, and providestransmit power level P_(eb)(n) to TX data processor 280. Processor 280then transmits codewords at transmit power of P_(eb)(n).

In the design shown in FIG. 2, RL power control is performed basedsolely on power control feedback from serving sector 110 x. Thisfeedback may comprise PC commands in the up-down PC mode and erasureindications in the erasure-based PC mode. This design may simplify RLpower control since the transmit power of terminal 120 is adjusted basedon feedback from one source.

RL power control may also be performed based on feedback from multiplesectors. In another design of the up-down PC mode, multiple sectors mayestimate the received signal quality for terminal 120 and send PCcommands to the terminal. Terminal 120 may then adjust its transmitpower based on the PC commands received from all sectors. Terminal 120may apply an OR-of-the-down rule and may reduce its transmit powerwhenever any sector sends a DOWN command. Terminal 120 may also combinethe received PC commands in other manners. In another design of theerasure-based PC mode, terminal 120 may adjust its transmit power basedon the erasure indications received from multiple sectors. In yetanother design, a hybrid PC mode may be supported, and terminal 120 mayadjust its transmit power based on a combination of PC commands anderasure indications. RL power control may also be performed in othermanners.

In one design, the active set includes the serving and non-servingsectors, as described above. In another design, the active set mayinclude multiple synchronous subsets. The serving sector may be selectedfrom one of the synchronous subsets, and the best sector in eachremaining synchronous subset (if any) may be identified, e.g., based onthe erasure rate for the sector. The terminal may respond to feedback(e.g., PC commands and/or erasure indications) from the serving sectoras well as feedback from the best sector in each remaining synchronoussubset. To avoid possible ambiguities, each sector may use the up-downPC mode for terminals being served by that sector on the reverse linkand may use the erasure-based PC mode for other terminals having thatsector in their active sets.

In another aspect, RL handoff for a terminal is supported based onerasure indications sent by the serving and non-serving sectors. Handoffor handover refers to the process of being handed off from one servingsector to another serving sector. On the reverse link, different sectorstypically observe different received signal qualities for the terminaldue to different path losses and/or interference levels. It is desirablefor the sector observing the best received signal quality to serve theterminal. In general, the sectors may estimate the received signalquality for the terminal based on any transmission sent by the terminal.However, if the terminal is already transmitting codewords for otherpurposes, then the sectors may efficiently use these codewords toestimate the received signal quality for the terminal. The erasureindications sent by the sectors would then represent feedback indicatingthe received signal quality measured by the sectors for the terminal.The terminal may use the erasure indications to select the best sectorto serve the terminal on the reverse link.

In the design shown in FIG. 2, an RL handoff processor 290 receives theerasure indications from serving sector 110 x as well as non-servingsector 110 a through 110 m. Processor 290 identifies the sectorobserving the best received signal quality for terminal 120 based on thereceived erasure indications, as described below. Processor 290 maygenerate a handoff request if another sector observes better receivedsignal quality for terminal 12 than the current serving sector.

In one design, RL power control may be performed based on PC commands,and RL handoff may be performed based on erasure indications. In anotherdesign, RL power control and handoff may both be performed based onerasure indications. In other designs, RL power control and handoff maybe performed based on other feedback from the sectors.

The up-down PC mode and the erasure-based PC mode may be implemented invarious manners. Exemplary designs for the two PC modes are describedbelow.

FIG. 3 shows a design of a power control mechanism 300 for the up-downPC mode. Power control mechanism 300 includes an inner loop 310, anouter loop 312, and a third loop 314. Inner loop 310 operates betweenserving sector 110 x and terminal 120. Outer loop 312 and third loop 314are maintained by serving sector 110 x. At terminal 120, inner loop 310is supported by up-down PC mode processor 260, which includes a PCcommand processor 262 and a TX power adjustment unit 264.

Inner loop 310 adjusts the transmit power of terminal 120 to maintainthe received signal quality close to a target signal quality at servingsector 110 x. Signal quality may be quantified by a signal-to-noiseratio (SNR), a signal-to-noise-and-interference ratio (SINR), acarrier-to-interference ratio (C/I), an energy-per-symbol-to-noise ratio(Es/No), and so on. For clarity, SNR is used to denote signal quality inthe description below. At serving sector 110 x, an SNR estimator 220estimates the received SNR of terminal 120 (e.g., based on the controlchannel carrying the codewords) and provides the received SNR. SNRestimator 220 may average SNR estimates over multiple frames to obtainan improved estimate of the received SNR. SNR estimator 220 may alsodiscard SNR estimates for frames in which the received codewords areerased. A PC command generator 222 obtains the received SNR and a targetSNR, compares the received SNR against the target SNR, and generates PCcommands, as follows:If SNR_(rx)(n)<SNR_(target), then PC command=UP command, else  (Eq (1)If SNR_(rx)(n)≧SNR_(target), then PC command=DOWN command,where SNR_(rx)(n) is the received SNR in frame n and SNR_(target) is thetarget SNR. Serving sector 110 x transmits the PC commands to terminal120.

At terminal 120, PC command processor 262 receives the PC commands sentby serving sector 110 x and makes a decision on each received PCcommand. A PC decision may be either an UP decision if the received PCcommand is deemed to be an UP command or a DOWN decision if the receivedPC command is deemed to be a DOWN command. Adjustment unit 264 may thenadjust the transmit power of terminal 120 based on the PC decisions fromprocessor 262, as follows:

$\begin{matrix}{{P_{ud}\left( {n + 1} \right)} = \left\{ \begin{matrix}{{P_{ud}(n)} + {\Delta\; P}} & {{{for}\mspace{14mu}{an}\mspace{14mu}{UP}\mspace{14mu}{decision}},} \\{{P_{ud}(n)} - {\Delta\; P}} & {{{for}\mspace{14mu} a\mspace{14mu}{DOWN}\mspace{20mu}{decision}},}\end{matrix} \right.} & {{Eq}\mspace{14mu}(2)}\end{matrix}$where P_(ud)(n) is the transmit power in frame n, and

ΔP is the step size for adjusting the transmit power in the up-down PCmode.

The transmit power P_(ud)(n) and the step size ΔP are given in units ofdecibels (dB). In the design shown in equation (2), the transmit poweris increased or decreased by the same step size (e.g., 0.5 dB, 1.0 dB,or some other value), which may be selected to provide good performancefor RL power control. In another design, the transmit power is adjustedby different up and down step sizes. The transmit power P_(ud)(n) mayalso be maintained at the same level if a received PC command is deemedto be too unreliable. Processor 280 generates codewords and transmitsthese codewords at transmit power of P_(ud)(n) to serving sector 110 xand non-serving sectors 110 a through 110 m (not shown in FIG. 3).

Outer loop 312 adjusts the target SNR based on received codewords toachieve the target erasure rate for the codewords sent by terminal 20.At serving sector 110 x, a metric computation unit 224 computes a metricfor each received codeword. An erasure detector 226 performs erasuredetection for each received codeword based on the metric and an erasurethreshold, as described below, and provides the status of each receivedcodeword, which may be either erased or non-erased. A target SNRadjustment unit 228 obtains the status of each received codeword and, inone design, may adjust the target SNR, as follows:

$\begin{matrix}{{{SNR}_{target}\left( {k + 1} \right)} = \left\{ \begin{matrix}{{{{SNR}_{target}(k)} + {\Delta\;{SNR}_{up}}},} & {{{for}\mspace{14mu}{an}\mspace{14mu}{erased}\mspace{14mu}{codeword}},} \\{{{{SNR}_{target}(k)} - {\Delta\;{SNR}_{dn}}},} & {{{for}\mspace{14mu}{an}\mspace{14mu}{non}\text{-}{erased}\mspace{14mu}{codeword}},}\end{matrix} \right.} & {{Eq}\mspace{14mu}(1)}\end{matrix}$where SNR_(target)(k) is the target SNR in update interval k,

ΔSNR_(up) is an up step size for the target SNR, and

ΔSNR_(dn) is a down step size for the target SNR.

The target SNR and the up and down step sizes are given in units of dB.

The ΔSNR_(up) and ΔSNR_(dn) step sizes may be set as follows:

$\begin{matrix}{{{\Delta\;{SNR}_{up}} = {\Delta\;{{SNR}_{dn} \cdot \left( \frac{1 - \Pr_{erasure}}{\Pr_{erasure}} \right)}}},} & {{Eq}\mspace{14mu}(4)}\end{matrix}$where Pr_(erasure) is the target erasure rate. As an example, if thetarget erasure rate is 10%, then the up step size is 9 times the downstep size. If the up step size is 0.5 dB, then the down step size isapproximately 0.056 dB.

In another design, serving base station 110 x measures the erasure rateover a window of erased codewords and adjusts the target SNR based onthe difference between the measured erasure rate and the target erasurerate. The target SNR may be adjusted using equal or different up anddown step sizes.

In one design, the erasure threshold is fixed, and a suitable thresholdvalue may be determined based on computer simulation, empiricalmeasurements, and/or some other means. In another design, the erasurethreshold is adjusted with a closed loop to achieve a target conditionalerror rate Pr_(error) for the codewords. The conditional error rate isthe probability of error conditioned on non-erased codewords, whichmeans: given that a received codeword is declared to be non-erased, theprobability of the received codeword being decoded in error isPr_(error). A low Pr_(error) (e.g., 1% or 0.1%) corresponds to highdegree of confidence in the decoding result when a non-erased codewordis declared.

Third loop 314 adjusts the erasure threshold based on received knowncodewords to achieve the target conditional error rate. Terminal 120 maytransmit a known codeword periodically or whenever directed. At servingsector 110 x, metric computation unit 224 and erasure detector 226perform erasure detection for each received known codeword in the samemanner as for other received codewords. Erasure detector 226 providesthe status of each received known codeword. A decoder 230 decodes eachreceived known codeword deemed to be non-erased and provides thecodeword status, which may be: (1) “erased”, (2) “good” if the receivedknown codeword is non-erased and decoded correctly, or (3) “bad” if thereceived known codeword is non-erased but decoded in error. In onedesign, an erasure threshold adjustment unit 232 may adjust the erasurethreshold based on the status of the received known codewords, asfollows:

$\begin{matrix}{{{TH}_{erasure}\left( {j + 1} \right)} = \left\{ \begin{matrix}{{{{TH}_{erasure}(j)} - {\Delta\;{TH}_{dn}}},} & {{{for}\mspace{14mu} a\mspace{14mu}{good}\mspace{14mu}{codeword}},} \\{{{{TH}_{erasure}(j)} + {\Delta\;{TH}_{up}}},} & {{{for}\mspace{14mu} a\mspace{14mu}{bad}\mspace{14mu}{codeword}},{and}} \\{{{TH}_{erasure}(j)},} & {{{for}\mspace{14mu}{an}\mspace{14mu}{erased}\mspace{14mu}{codeword}},}\end{matrix} \right.} & {{Eq}\mspace{14mu}(2)}\end{matrix}$where TH_(erasure)(j) is the erasure threshold in update interval j,

ΔTH_(up) is an up step size for the erasure threshold, and

ΔTH_(dn) is a down step size for the erasure threshold.

The design in equation (5) assumes that a larger metric for a receivedcodeword corresponds to higher degree of confidence. In this case, theerasure threshold is increased by ΔTH_(up) for each received knowncodeword that is “bad”. The higher erasure threshold corresponds to amore stringent erasure detection criterion and results in a receivedcodeword being more likely to be deemed erased, which in turn results inthe received codeword being more likely to be decoded correctly whendeemed to be non-erased. The erasure threshold is decreased by ΔTH_(dn)for each received known codeword that is “good” and is maintained forreceived known codewords that are erased.

The ΔTH_(up) and ΔTH_(dn) step sizes may be set as follows:

$\begin{matrix}{{\Delta\;{TH}_{up}} = {\Delta\;{{TH}_{dn} \cdot {\left( \frac{1 - \Pr_{error}}{\Pr_{error}} \right).}}}} & {{Eq}\mspace{14mu}(6)}\end{matrix}$As an example, if the target conditional error rate is 1%, then the upstep size is 99 times the down step size. The magnitude of ΔTH_(up) andΔTH_(dn) may be selected based on the desired convergence rate for thethird loop and/or other factors.

In another design, serving base station 110 x measures the error rate(or a false alarm rate) and adjusts the erasure threshold based on thedifference between measured error rate and a target error rate (orbetween the false alarm rate and a target false alarm rate). The erasurethreshold may be adjusted with equal or different up and down thresholdstep sizes.

The erasure threshold may be adjusted inv arious manners. In one design,serving section 110 x maintains a separate third loop for each terminaland adjusts the erasure threshold to achieve the desired performance forthat terminal. In another design, serving sector 110 x maintains asingle third loop for all terminals and adjusts the erasure thresholdbased on known codewords received from these terminals. In yet anotherdesign, serving section 110 x maintains a separate third loop for eachgroup of terminals with similar performance and adjusts the erasurethreshold based on known codewords received from all terminals in thegroup.

The erasure rate, conditional error rate, erasure threshold, andreceived SNR are typically related. For a given erasure threshold and agiven received SNR, there exist a specific erasure rate and a specificconditional error rate. By changing the erasure threshold via third loop314, a tradeoff may be made between the erasure rate and the conditionalerror rate.

Inner loop 310, outer loop 312, and third loop 314 may operate atdifferent rates. Inner loop 310 may be updated whenever the received SNRis available. Outer loop 312 may be updated whenever a codeword isreceived. Third loop 314 may be updated whenever a known codeword isreceived. The update rates for the three loops may be selected toachieve the desired performance for RL power control.

FIG. 4 shows a design of a power control mechanism 400 for theerasure-based PC mode. Power control mechanism 400 includes a first loop410 and a second loop 412. First loop 410 operates between servingsector 110 x and terminal 120, and second loop 412 is maintained byserving sector 110 x. At terminal 120, first loop 410 is supported byerasure-based PC mode processor 270, which includes an erasureindication processor 272 and a TX power adjustment unit 274.

First loop 410 adjusts the transmit power of terminal 120 to achieve thetarget erasure rate. At serving sector 110 x, metric computation unit224 computes the metric for each received codeword. Erasure detector 226performs erasure detection for each received codeword based on themetric and the erasure threshold, as described below, and generates anerasure indication that indicates whether the received codeword iserased or non-erased. Serving sector 110 x transmits the erasureindications to terminal 120.

At terminal 120, erasure indication processor 272 receives the erasureindications sent by serving sector 110 x and makes a decision of erasedor non-erased for each received erasure indication. Adjustment unit 274may adjust the transmit power of terminal 120 based on the erasuredecisions from processor 272, as follows:

$\begin{matrix}{{P_{eb}\left( {n + 1} \right)} = \left\{ \begin{matrix}{{P_{eb}(n)} + {\Delta\; P_{up}}} & {{{for}\mspace{14mu}{an}\mspace{14mu}{erased}\mspace{14mu}{decision}},} \\{{P_{eb}(n)} - {\Delta\; P_{dn}}} & {{{for}\mspace{14mu} a\mspace{14mu}{non}\text{-}{erased}\mspace{20mu}{decision}},}\end{matrix} \right.} & {{Eq}\mspace{14mu}(7)}\end{matrix}$where ΔP_(up) is an up step size for an erased decision, and

ΔP_(dn) is a down step size a non-erased decision.

The ΔP_(up) and ΔP_(dn) step sizes may be set based on the targeterasure rate, as follows:

$\begin{matrix}{{\Delta\; P_{up}} = {\Delta\;{P_{dn} \cdot {\left( \frac{1 - \Pr_{erasure}}{\Pr_{erasure}} \right).}}}} & {{Eq}\mspace{14mu}(8)}\end{matrix}$

Serving sector 110 x may broadcasts the ΔP_(up) and/or ΔP_(dn) stepsizes to the terminals within its coverage area. In a given deployment,the target erasure rate may change very slowly. Thus, the overhead ofbroadcasting the ΔP_(up) and/or ΔP_(dn) step sizes may be a smallpercentage of the total overhead.

Second loop 412 adjusts the erasure threshold based on received knowncodewords to achieve the target conditional error rate. Second loop 412operates as described above for third loop 314 in FIG. 3.

First loop 410 and second loop 412 may operate at different rates. Firstloop 410 may be updated whenever a codeword is received. Second loop 412may be updated whenever a known codeword is received.

In the designs shown in FIGS. 3 and 4, the desired level of performanceis quantified by a target erasure rate and a target conditional errorrate. Performance may also be quantified by other measures such as,e.g., a target false alarm probability, which is the probability isdeclaring a non-erased codeword when none was sent. The power controlmechanisms may be designed in accordance with the measure(s) used toquantify performance.

Various factors may be considered in selecting either the up-down PCmode or the erasure-based PC mode for use. For example, a PC mode may beselected based on the target erasure rate, convergence rate, and/orother factors. The erasure-based PC mode may be similar to the up-downPC mode if the target erasure rate is 50%. These two PC modes may havedifferent characteristics if the target erasure rate is something otherthan 50%. The erasure-based PC mode may be used to directly achieve thetarget erasure rate without using an outer loop. However, the use ofdifferent ΔP_(up) and ΔP_(dn) step sizes in the erasure-based PC modemay result in (1) slower convergence to the proper transmit power leveland (2) a wider distribution of received SNR. The erasure rate may alsobe sensitive to errors in detecting the erasure indications, especiallywhen targeting very high or very low erasure rates, e.g., 1% or 10%. Theup-down PC mode utilizes equal up and down step sizes ΔP regardless ofthe target erasure rate. Consequently, the up-down PC mode may be ableto achieve (1) faster convergence to the proper transmit power level and(2) a more narrow distribution of received SNR.

In one design, a PC mode may be selected for each terminal. In anotherdesign, a PC mode is selected for each sector and is used for allterminals served by that sector. In yet another design, a PC mode isselected for each group of sectors or an entire network. In all designs,the selected PC mode may be signaled to the terminal(s) via an overheadmessage parameter, e.g., the RLCtrlPCMode bit described above.

A terminal may ascertain the PC mode to use for power control by readingthe overhead message parameter. If this parameter indicates the up-downPC mode, then the terminal may adjust its transmit power with equal upand down step sizes based on PC commands received from the servingsector. If the parameter indicates the erasure-based PC mode, then theterminal may treat the erasure indications from the serving sector aspower control commands and may adjust its transmit power with differentup and down step sizes based on the received erasure indications.

The RL power control described above allows for reliable operation ofthe control channel used to send the codewords. The transmit power ofthis control channel may be used as a reference power level for othercontrol channels and data channels.

2. Erasure Detection

Erasure detection may be performed in various manners depending on howthe codewords are generated and the metric selected for use. Severalexemplary schemes for erasure detection are described below.

In one design, a terminal maps a CQI report (or a signaling message) ofL bits to one of 2^(L) possible Walsh codes of length 2^(L). Theterminal then transmits the mapped Walsh code as the codeword for theCQI report. The terminal may scramble the codeword prior totransmission. A sector receives the transmitted codeword and performsthe complementary descrambling prior to detection of the codeword.

In one design, the sector performs detection by despreading the receivedcodeword with each of the 2^(L) possible Walsh codes, as follows:

$\begin{matrix}\begin{matrix}{{{M_{\ell}(n)} = {\sum\limits_{i = 1}^{2^{L}}{{r\left( {n,i} \right)} \cdot {w_{\ell}(i)}}}},} & {{{{for}\mspace{14mu}\ell} = 1},\ldots\mspace{11mu},2^{L},}\end{matrix} & {{Eq}\mspace{14mu}(3)}\end{matrix}$where r (n,i) is the i-th received sample in frame n,

w_(l)(i) is the i-th chip of Walsh code_(l), and

M_(l)(n) is the metric value for Walsh code _(l) in frame n.

The sector obtains 2^(L) metric values for the 2^(L) possible Walshcodes that could have been transmitted. The sector may compare eachmetric value against the erasure threshold, as follows:If M_(l)(n)>TH_(erasure), then declare detected Walsh code_(l.)  Eq (4)

If the codeword was transmitted with sufficient power, then only onemetric value will likely exceed the erasure threshold. In this case, theWalsh code for this metric value may be provided as the decoded word,and a non-erased codeword may be declared. However, if all 2^(L) metricvalues are below the erasure threshold, then an erased codeword may bedeclared. If multiple metric values exceed the erasure threshold, thenan error event may be declared since only one Walsh code could have beentransmitted. This error event may be due to noise and interferenceobserved by the sector and may be more likely with a low erasurethreshold.

In another design, the sector performs detection by computing theEuclidean distance between the received codeword and each of the 2^(L)possible valid codewords in the codebook, e.g., as shown in equation(9). The sector may then derive a metric as follows:

$\begin{matrix}{{{M(n)} = \frac{d_{1}(n)}{d_{2}(n)}},} & {{Eq}\mspace{14mu}(11)}\end{matrix}$where d₁(n) is the Euclidean distance between the received codeword inframe n and the nearest valid codeword, and

d₂(n) is the Euclidean distance between the received codeword in frame nand the next nearest valid codeword.

The sector may then compare the metric against the erasure threshold, asfollows:If M(n)<TH_(erasure), then declare a non-erased codeword, else  Eq (12)If M(n)≧TH_(erasure), then declare an erased codeword.

Other metrics may also be used for erasure detection. In general, ametric may be defined based on any reliability function f(r,C), where ris a received codeword and C is a codebook of all possible codewords.The function f(r,C) should be indicative of the quality/reliability ofthe received codeword and should have the proper characteristics, e.g.,monotonic with detection reliability.

3. RL Handoff

Terminal 120 may use the erasure indications from serving sector 110 xand non-serving sector 110 a through 110 m for RL handoff. Terminal 120may determine the erasure rate observed by each sector for terminal 120based on the erasure indications received from that sector. For eachsector, terminal 120 may determine whether each erasure indicationreceived from that sector indicates an erased codeword or a non-erasedcodeword. Terminal 120 may count the number of erased codewords within apredetermined time window to determine the erasure rate for the sector.Terminal 120 may identify the sector with the lowest erasure rate andmay select this sector as the RL serving sector.

Terminal 120 may send a handoff request message to the current servingsector and/or the newly selected sector. In one design, terminal 120sends a request for reverse link resources whenever terminal 120 wantsto transmit on the reverse link. Terminal 120 may send this resourcerequest to either (1) the current serving sector by applying anidentification code for this sector or (2) the newly selected sector byapplying an identification code for this new sector. The transmission ofthe resource request to the newly selected sector may be considered as ahandoff request to the new sector. The handoff request may also be sentin other manners.

RL handoff may also be initiated by the system. In one design, thesectors in the active set of terminal 120 send erasure indications to adesignated entity, e.g., system controller 130 in FIG. 1. The designatedentity may determine the sector observing the best reverse link forterminal 120 and may select this sector as the RL serving sector for theterminal. The current serving sector and/or the newly selected sectormay send signaling to terminal 120 to convey the RL handoff.

4. System

FIG. 5 shows a design of a process 500 performed by a base station(e.g., a serving base station) for RL power control of a terminal.Signaling indicating a PC mode selected from among multiple PC modes issent (block 510). The multiple PC modes may include the up-down PC mode,the erasure-based PC mode, and/or some other PC mode. The signaling maybe an RLCtrlPCMode bit or some other type of signaling. Power controlfeedback for the terminal is then generated in accordance with theselected PC mode (block 520). The power control feedback is used toadjust the transmit power of the terminal and may comprise PC commands,erasure indications, and/or other information. The power controlfeedback is sent to the terminal (block 540). Up and/or down step sizesused for adjusting transmit power may also be sent to the terminal orbroadcast to all terminals.

For block 520, a determination is made whether the up-down PC mode orthe erasure-based PC mode is selected (block 522). If the up-down PCmode is selected, then the received signal quality for the terminal isestimated (block 524), and PC commands are generated based on thereceived signal quality and a target signal quality (block 526). Thetarget signal quality may be adjusted to achieve a target level ofperformance, e.g., a target erasure rate (block 528). If theerasure-based PC mode is selected, then codewords are received from theterminal (block 534). Whether each received codeword is erased ornon-erased is determined (block 536), and erasure indications for thereceived codewords are sent (block 538).

FIG. 6 shows a design of an apparatus 600 supporting RL power controlfor a terminal. Apparatus 600 includes means for sending signalingindicating a PC mode selected from among multiple PC modes (module 610),means for generating power control feedback for the terminal inaccordance with the selected PC mode (module 620), and means for sendingthe power control feedback to the terminal (module 640). The means forgenerating power control feedback includes means for determining whetherto use the up-down PC mode or the erasure-based PC mode (module 622).For the up-down PC mode, the means for generating power control feedbackincludes means for estimating the received signal quality for theterminal (module 624), means for generating PC commands based on thereceived signal quality and a target signal quality (module 626), andmeans for adjusting the target signal quality to achieve a target levelof performance, e.g., a target erasure rate (module 628). For theerasure-based PC mode, the means for generating power control feedbackincludes means for receiving codewords from the terminal (module 634),means for determining whether each received codeword is erased ornon-erased (module 636), and means for sending erasure indications forthe received codewords (module 638). Modules 610 through 640 maycomprise processors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

FIG. 7 shows a design of a process 700 performed by a terminal for RLpower control. Initially, signaling indicating a PC mode selected fromamong multiple PC modes is received (block 710). Transmit power is thenadjusted in accordance with the selected PC mode (block 720).

For block 720, a determination is made whether the up-down PC mode orthe erasure-based PC mode is selected (block 722). If the up-down PCmode is selected, then PC commands are received (block 724), and thetransmit power is adjusted in accordance with the received PC commands(block 726). The transmit power may be (1) increased by an up step if areceived PC command is an up command or (2) decreased by a down step ifthe received PC command is a down command. The up and down step sizesmay be equal in the up-down PC mode. If the erasure-based PC mode isselected, then erasure indications are received for codewords sent via acommunication channel (block 734), and the transmit power is adjusted inaccordance with the received erasure indications (block 736). Thetransmit power may be (1) increased by an up step if a received erasureindication indicates an erased codeword or (2) decreased by a down stepif the received erasure indication indicates a non-erased codeword. Theup and down step sizes may be different in the erasure-based PC mode andmay be selected based on the target erasure rate.

Codewords are sent at the transmit power adjusted in accordance with theselected PC mode (block 740). The transmit power for other transmissionsmay also be adjusted based on the transmit power for the codewords.

FIG. 8 shows a design of an apparatus 800 for performing RL powercontrol for a terminal. Apparatus 800 includes means for receivingsignaling indicating a PC mode selected from among multiple PC modes(module 810), means for adjusting transmit power in accordance with theselected PC mode (module 820), and means for sending codewords at thetransmit power adjusted in accordance with the selected PC mode (module840). The means for adjusting transmit power includes means fordetermining whether to use the up-down PC mode or the erasure-based PCmode (module 822). For the up-down PC mode, the means for adjustingtransmit power includes means for receiving PC commands (module 824) andmeans for adjusting the transmit power in accordance with the receivedPC commands (module 826). For the erasure-based PC mode, the means foradjusting transmit power includes means for receiving erasureindications for codewords sent via a communication channel (module 834)and means for adjusting the transmit power in accordance with thereceived erasure indications (module 836). Modules 810 through 840 maycomprise processors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

FIG. 9 shows a design of a process 900 performed by a terminal for RLpower control and handoff. Transmit power is adjusted based on PCcommands received from a first set of at least one base station (block912). Handoff is performed based on erasure indications received from asecond set of at least one base station (block 914). The first set mayinclude only the serving base station. The second set may include theserving base station and possibly other base stations:

The terminal transmits codewords on the reverse link. For RL handoff,erasure indications for the codewords may be received from the secondset of base station(s). An erasure rate may be determined for each basestation in the second set based on the erasure indications received fromthat base station. The base station with the lowest erasure rate may beselected as a new serving base station, and handoff may be performed tothe selected base station. For RL power control, the transmit power ofthe terminal may be increased by an up step if a received PC command isan up command or decreased by a down step if the received PC command isa down command.

FIG. 10 shows a design of an apparatus 1000 for performing RL powercontrol and handoff. Apparatus 1000 includes means for adjustingtransmit power based on PC commands received from a first set of atleast one base station (module 1012) and means for performing handoffbased on erasure indications received from a second set of at least onebase station (module 1014). Modules 1012 and 1014 may compriseprocessors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

FIG. 11 shows a block diagram of a design of terminal 120, serving basestation 110 x, and non-serving base station 110 m in FIG. 1. At servingbase station 110 x, a TX data processor 1114 x receives traffic datafrom a data source 1112 x and signaling from a controller/processor 1130x and a scheduler 1134 x. Controller/processor 1130 x may providefeedback (e.g., PC commands and/or erasure indications) to adjust thetransmit power of the terminals communicating with base station 110 x,and scheduler 1134 x may provide assignments of data channels and/orsubcarriers to the terminals. TX data processor 1114 x processes (e.g.,encodes, interleaves, and symbol maps) the traffic data and signalingand provides symbols. A modulator (Mod) 1116 x performs modulation onthe symbols (e.g., for CDMA, OFDMA, and/or other radio technologies) andprovides output chips. A transmitter (TMTR) 1118 x conditions (e.g.,converts to analog, amplifies, filters, and frequency upconverts) theoutput chips and generates a forward link signal, which is transmittedvia an antenna 1120 x.

Non-serving base station 110 m similar processes traffic data andsignaling for terminals being served by base station 110 m and terminalshaving base station 110 m in their active sets. The traffic data andsignaling are processed by a TX data processor 1114 m, modulated by amodulator 1116 m, conditioned by a transmitter 1118 m, and transmittedvia an antenna 1120 m. Data source 1112 provides data to TX dataprocessor 1114 m. Receiver 1140 m, Demodulator 1142 m, RX data processor1144 m, and Data sink 1146 m provide similar functions as thosedescribed for Receiver 1140 x, Demodulator 1142 x, RX data processor1144 x, and Data sink 1146 x respectively.

At terminal 120, an antenna 1152 receives the forward link signals frombase stations 110 x and 110 m and possibly other base stations. Areceiver 1154 conditions (e.g., filters, amplifies, frequencydownconverts, and digitizes) a received signal from antenna 1152 andprovides samples. A demodulator (Demod) 1156 performs demodulation(e.g., for CDMA, OFDMA, and/or other radio technologies) and providessymbol estimates. An RX data processor 1158 processes (e.g., symboldemaps, deinterleaves, and decodes) the symbol estimates, providesdecoded data to a data sink 1160, and provides detected signaling (e.g.,RLCtrlPCMode bit, PC commands, erasure indications, and so on) to acontroller/processor 1170.

On the reverse link, a TX data processor 1182 processes traffic datafrom a data source 1180 and signaling (e.g., codewords, handoff request,and so on) from controller/processor 1170 and generates symbols. Thesymbols are modulated by a modulator 1184 and conditioned by atransmitter 1186 to generate a reverse link signal, which is transmittedfrom antenna 1152. Controller 1170 may provide an indication of thetransmit power level to use for transmission.

At serving base station 110 x, the reverse link signals from terminal120 and other terminals are received by antenna 1120 x, conditioned by areceiver 1140 x, demodulated by a demodulator 1142 x, and processed byan RX data processor 1144 x. Processor 1144 x provides decoded data to adata sink 1146 x and detected signaling (e.g., codewords) tocontroller/processor 1130 x. Receiver 1140 x may estimate the receivedsignal quality for each terminal and may provide this information tocontroller/processor 1130 x. Controller/processor 1130 x may derive PCcommands and/or erasure indications for each terminal, as describedabove. Non-serving base station 110 m may similarly detect signaling(e.g., codewords and handoff request) sent by terminal 120 and may senderasure indications to the terminal.

Controllers/processors 1130 x, 1130 m and 1170 direct the operations ofvarious processing units at base stations 110 x and 110 m and terminal120, respectively. These controllers/processors may also perform variousfunctions for power control and handoff. For example,controller/processor 1130 x may implement some or all of units 220through 2232 shown in FIGS. 3 and 4 for base station 110 x. Controller1170 may implement some or all of units 258 through 290 shown in FIGS. 2through 4 for terminal 120. Controller 1130 x may also implement process500 in FIG. 5. Controller 1170 may also implement processes 700 and/or900 in FIGS. 7 and 9. Memories 1132 x, 1132 m and 1172 store data andprogram codes for base stations 110 x and 110 m and terminal 120,respectively. Schedulers 1134 x and 1134 m schedule terminalscommunicating with base stations 110 x and 110 m, respectively, andassign data channels and/or subcarriers to the scheduled terminals.

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, firmware,software, or a combination thereof. For a hardware implementation, theprocessing units used to perform power control and handoff may beimplemented within one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, micro-controllers,microprocessors, electronic devices, other electronic units designed toperform the functions described herein, or a combination thereof.

For a firmware and/or software implementation, the techniques may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The firmware and/or softwarecodes may be stored in a memory (e.g., memory 1132 x, 1132 m or 1172 inFIG. 11) and executed by a processor (e.g., processor 1130 x, 1130 m or1170). The memory may be implemented within the processor or external tothe processor.

Headings are included herein for reference and to aid in locatingcertain sections. These headings are not intended to limit the scope ofthe concepts described therein under, and these concepts may haveapplicability in other sections throughout the entire specification.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples described herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

1. An apparatus comprising: at least one processor configured to receivesignaling indicating power control (PC) modes selected from amongmultiple PC modes, wherein the multiple PC modes comprise an up-down PCmode and an erasure-based PC mode, wherein the signaling are receivedfrom at least one serving sector and one neighboring sector, and whereinthe signaling from at least two different sectors indicate different PCmodes, and to adjust transmit power in accordance with a determined PCmode, wherein the determined PC mode is based upon the received PC modesand their corresponding erasure indications, wherein to adjust transmitpower further comprises to adjust the transmit power by an up power stepsize computed by a product of a down power step size and a firstfunction of a target erasure rate in response to an erased decisionbased on the erasure indications, and to adjust the transmit power by adown power step size computed by a product of an up power step size anda second function of the target erasure rate in response to a non-eraseddecision based on the erasure indications; and a memory coupled to theat least one processor, wherein the memory is configured to store themultiple PC modes.
 2. The apparatus of claim 1, wherein the determinedPC mode is the up-down PC mode, and wherein the at least one processoris configured to adjust the transmit power in accordance with receivedPC commands.
 3. The apparatus of claim 2, wherein the at least oneprocessor is configured to increase the transmit power by an up step ifa received PC command is an up command, and to decrease the transmitpower by a down step if the received PC command is a down command. 4.The apparatus of claim 3, wherein the up step is equal to the down step.5. The apparatus of claim 1, wherein the determined PC mode is theerasure-based PC mode, and wherein the at least one processor isconfigured to receive erasure indications for codewords sent via acommunication channel, and to adjust the transmit power in accordancewith the received erasure indications.
 6. The apparatus of claim 5,wherein the at least one processor is configured to increase thetransmit power by an up step if a received erasure indication indicatesan erased codeword, and to decrease the transmit power by a down step ifthe received erasure indication indicates a non-erased codeword.
 7. Theapparatus of claim 6, wherein the up step and the down step aredetermined by the target erasure rate.
 8. The apparatus of claim 1,wherein the at least one processor is configured to send codewords atthe transmit power adjusted in accordance with the determined PC mode.9. A method comprising: receiving signaling indicating power control(PC) modes selected from among multiple PC modes, wherein the multiplePC modes comprise an up-down PC mode and an erasure-based PC mode,wherein the signaling are received from at least one serving sector andone neighboring sector, and wherein the signaling from at least twodifferent sectors indicate different PC modes; and adjusting transmitpower in accordance with a determined PC mode, wherein the determined PCmode is based upon the received PC modes and their corresponding erasureindications, wherein adjusting transmit power further comprisesadjusting the transmit power by an UP power step size computed by aproduct of a down power step size and a first function of a targeterasure rate in response to an erased decision based on the erasureindications, and adjusting the transmit power by a down power step sizecomputed by a product of an up power step size and a second function ofthe target erasure rate in response to a non-erased decision based onthe erasure indications.
 10. The method of claim 9, wherein theadjusting the transmit power in accordance with the determined PC modecomprises adjusting the transmit power in accordance with received PCcommands.
 11. The method of claim 9, wherein the adjusting the transmitpower in accordance with the determined PC mode comprises receivingerasure indications for codewords sent via a communication channel, andadjusting the transmit power in accordance with the received erasureindications.
 12. An apparatus comprising: means for receiving signalingindicating power control (PC) modes selected from among multiple PCmodes, wherein the multiple PC modes comprise an up-down PC mode and anerasure-based PC mode, wherein the signaling are received from at leastone serving sector and one neighboring sector, and wherein the signalingfrom at least two different sectors indicate different PC modes; andmeans for adjusting transmit power in accordance with a determined PCmode, wherein the determined PC mode is based upon the received PC modesand their corresponding erasure indications, wherein means for adjustingtransmit power further comprises means for adjusting the transmit powerby an up power step size computed by a product of a down power step sizeand a first function of a target erasure rate in response to an eraseddecision based on the erasure indications, and means for adjusting thetransmit power by a down power step size computed by a product of an uppower step size and a second function of the target erasure rate inresponse to a non-erased decision based on the erasure indications. 13.The apparatus of claim 12, wherein the means for adjusting the transmitpower in accordance with the determined PC mode comprises means foradjusting the transmit power in accordance with received PC commands.14. The apparatus of claim 12, wherein the means for adjusting thetransmit power in accordance with the determined PC mode comprises meansfor receiving erasure indications for codewords sent via a communicationchannel, and means for adjusting the transmit power in accordance withthe received erasure indications.
 15. A processor readable media,including a non-transitory computer readable storage device, for storinginstructions operable to: receive signaling indicating power control(PC) modes selected from among multiple PC modes, wherein the multiplePC modes comprise an up-down PC mode and, an erasure-based PC mode,wherein the signaling are received from at least one serving sector andone neighboring sector, and wherein the signaling from at least twodifferent sectors indicate different PC modes; and adjust transmit powerin accordance with a determined PC mode, wherein the determined PC modeis based upon the received PC modes and their corresponding erasureindications, wherein adjust transmit power further comprises adjust thetransmit power by an up power step size computed by a product of a downpower step size and a first function of a target erasure rate inresponse to an erased decision based on the erasure indications, andadjust the transmit power by a down power step size computed by aproduct of an up power step size and a second function of the targeterasure rate in response to a non-erased decision based on the erasureindications.
 16. The apparatus of claim 1, wherein the at least oneneighboring sector is a sector identified as a best sector, wherein thebest sector is identified based on its erasure rate.
 17. The method ofclaim 9, wherein the at least one neighboring sector is a sectoridentified as a best sector, wherein the best sector is identified basedon its erasure rate.
 18. The apparatus of claim 12, wherein the at leastone neighboring sector is a sector identified as a best sector, whereinthe best sector is identified based on its erasure rate.
 19. Theapparatus of claim 1, wherein the first function of the target erasurerate (TER) is a ratio of (1-TER) over TER.
 20. The apparatus of claim 1,wherein the second function of the target erasure rate (TER) is a ratioof TER over (1-TER).